Using a FileShare for the VPP files

I am trying to set up two load balanced servers to use a fileshare for the VPP files. I have mapped a network drive to the fileshare i Windows Explorer, but when I enter the path to the newtork drive in web.condig, physicalPath="Z:\VPP\acta.no\Global", I get an error: Could not find a part of the path 'Z:\VPP\acta.no\Global'

The "Network Service" account on my load balanced servers have read and write access to the share. Do I need to give more access rights?

Does anyone know what can be wrong? Is it not possible to use a fileshare for VPP in EPiServer CMS 5.2? The environment runs on Win 2003 Server.